hippocampus

American  

[hip-uh-kam-puhs] / ˌhɪp əˈkæm pəs /

noun

• hippocampi
  plural

1. Classical Mythology. a fish-tailed horse of the sea that was ridden by the sea gods.

2. Anatomy. an enfolding of cerebral cortex into the lateral fissure of a cerebral hemisphere, having a major role in learning, emotion, and memory, and named for the seahorse shape of its cross section.

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hippocampus British  

/ ˌhɪpəʊˈkæmpəs /

noun

1. a mythological sea creature with the forelegs of a horse and the tail of a fish

2. any marine teleost fish of the genus Hippocampus, having a horselike head See sea horse

3. an area of cerebral cortex that forms a ridge in the floor of the lateral ventricle of the brain, which in cross section has the shape of a sea horse. It functions as part of the limbic system

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hippocampus Scientific  

/ hĭp′ə-kăm′pəs /

• hippocampi
  plural

1. A convoluted, seahorse-shaped structure in the cerebral cortex of the temporal lobe of the brain, composed of two gyri with white matter above gray matter. It forms part of the limbic system and is involved in the processing of emotions and memory.

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Other Word Forms

Derived Forms

• hippocampal
  adjective

Inflected Forms

Nouns

• hippocampi
  plural

Etymology

Origin of hippocampus

First recorded in 1575–80; from Latin hippocampus, hippocampos, from Greek hippókampos, equivalent to hippo- hippo- + kámpos “sea monster”

Explanation

A hippocampus is a complex neural structure that's part of the brain. Your brain has two hippocampi, and they're important for memories and emotions. This word has a complex history. Originally, it meant a seahorse, and it has also meant a small fish that resembles a seahorse. That resemblance is why the brain structures known as the hippocampus major and hippocampus minor have that name: they look kind of like seahorses too. The hippocampi are found on the floor of your brain's ventricles, and they are vital to feeling and remembering. Without your hippocampi, you wouldn't be who you are.

Example Sentences

See Examples For:

hippocampus hippocampi

Young mice carrying APOE4 showed excessive neuronal activity in two areas of the hippocampus, a brain region central to memory.

From Science Daily ● Aug. 23, 2026

The hippocampus also contains the remarkable “place cells” – neurons that fire corresponding to a person’s thoughts about their position in space and, as recent research has shown, time.

From Science Daily ● Aug. 12, 2026

Older APOE2 knock-in mice had smaller nucleoli, higher levels of the nuclear scaffolding protein Lamin A/C, and better-preserved heterochromatin in the hippocampus than mice carrying APOE3 or APOE4.

From Science Daily ● Jul. 24, 2026

The hippocampus showed clear evidence of processing language in real time.

From Science Daily ● Jun. 29, 2026

My hippocampus turned and plunged into the waves.

From "The Sea of Monsters" by Rick Riordan

In the study, rats with perturbed hippocampi had to explore a maze and find a new path every day to collect a reward.

From Science Daily ● Oct. 23, 2023

For instance, in 2019 Noble and her colleagues, also using hair cortisol levels as markers of chronic stress, showed that higher levels were associated with smaller hippocampi, a part of the brain integral for memory.

From Scientific American ● Jun. 7, 2022

After nearly 1 month, the number of new neurons in the rodents’ hippocampi had doubled.

From Science Magazine ● Feb. 3, 2022

In the 1970s, O'Keefe had discovered neurons called place cells in the hippocampi of rats.

From Nature ● Oct. 5, 2014

Percy thought about the dazed telkhines, the Nereids and hippocampi, all swimming in bored, lazy circles.

From "The Mark of Athena" by Rick Riordan